Sulfurized calcium alkyl phenate detergents are well-known additive components for internal combustion engine lubricating oil compositions (or lubricants). Unreacted alkylphenol used in their manufacture may be present in the detergents. Such alkylphenols have undesirable properties such as giving rise to corrosion, and certain alkylphenols (e.g. nonylphenol and tetrapropenylphenol) are classified as reproductive toxins.
The art describes ways of overcoming this problem, a recent example being U.S. Pat. No. 8,772,209 B2 ('209), which describes protonating a phenate detergent with an acidic compound followed by removing unreacted phenol and protonated unsulfurized salt such as by distillation. A problem with this approach is that acid salts (e.g. Ca stearate) that are formed are neutralised to release organic acid into the lubricant, such acid being detrimental to the engine.
WO 2015/153160 A1 ('160) describes preparing an overbased sulfurized alkaline earth metal alkylphenate composition in oil. The composition is heated and subjected to steam stripping followed by filtration. The resulting product is stated to exhibit an improved rate and efficiency of filtration, but further states, without exemplification, that the product may also have a reduced level of free monomeric alkylphenate or alkylphenol (e.g. tetrapropenyl phenol (TPP)) than materials prepared by conventional means without the steam-stripping step. WO 2015/153160 A1 makes no mention of solvent addition to the resulting product before carrying out the stripping step.